1. Field of the Invention
This invention relates to rotating axially moving cutting tools having an axial core receiving central portion and particularly relates to such a tool adapted to remove a broken or otherwise useless steel stud from an aluminum aircraft engine cylinder jug without the necessity of first removing the cylinder jug from the aircraft engine.
2. Description of the Prior Art
Exhaust manifolds on reciprocating aircraft engines are generally of welded steel tube to withstand the high temperatures of exhaust gases created in the normal operation of the engine. The cylinders of the engine are usually forged steel cylinder barrels or liners force fit inside cast aluminum alloy cylinder heads commonly referred to as "jugs", the jugs having a plurality of air cooling fins extending outwardly as well as the intake and exhaust ports, valve seats, spark plugs, etc. Threaded steel studs securely seated in the aluminum jugs adjacent the exhaust ports project through holes in a flange joined to the end of the manifold. Appropriate nuts and washers secure the flange and, thus, the steel manifold to the aluminum jug.
During operation of the aircraft, the periodic heating and cooling of the engine and manifold coupled with the difference in the rate of thermal expansion of the two materials involved often leads to metal fatigue and ultimate failure of one or more of the studs. A problem thus results requiring the replacement of the broken steel stud with another of the same size as required by F.A.A. regulations.
Previously, it was necessary to remove the jug from the remainder of the aircraft engine, position the jug very carefully in a vertical milling machine or other similar precision drilling device, center punch and then drill out the stud with a conventional twist drill. The operation had to be executed with care as the aluminum jug is considerably softer than the hardened steel stud and the drill, following the path of least resistance, would wander off the steel into the aluminum. This would resul in a hole which was misaligned and too big to accept a new stud of the prescribed dimension. It is virtually impossible to perform this operation with a hand-held drill.
The whole operation of first removing the jug from the engine, boring out the broken stud, inserting a hollow, double-threaded adapter, seating a new stud and replacing the jug on the engine is so time-consuming, and thus, so costly, that when a stud fails, often the whole jug is simply replaced with a new one. This is expensive and undoubtedly a waste of resources.
No previous method or apparatus exists for successfully removing the broken stud from the aluminum jug while the jug is still on the engine, especialy if the engine is still in place in the aircraft. The use of a conventional extractor is unsatisfactory as the steel stud is usually bonded to the aluminum jug so well as to defy any attempt to back the broken stud out of the hole.
The hollow double-threaded adapters usually used in this operation are of the type marketed by Heli-Coil Corporation of Danbury, Connecticut.